Israel says its forces have fired "warning shots" into Syria after stray mortar fire from fighting in the civil war-hit nation struck the Israeli-occupied Golan Heights.

It was the first time Israel has been drawn into the unrest in the neighbouring country, and was the first Israeli fire directed at the Syrian military since the 1973 war.

The Israeli army said: "A mortar shell hit an IDF (Israeli Defence Force) post in the Golan Heights adjacent to the Israel-Syria border, as part of the internal conflict inside Syria.

"In response, IDF soldiers fired warning shots towards Syrian areas."

Sky's Middle East correspondent Sam Kiley said: "Sky sources tell me the warning shot was an anti-tank missile fired by Israel into Syrian territory, close to the crew that was identified as having fired this mortar round.

"So, already the Israelis are signalling that both sides should back off. They don't want another front line opening up in their ongoing conflicts, not least because in the last 24 hours there has been an escalation of violence in Gaza."

The shell overshot the Golan disengagement fence and exploded near a Jewish settlement without causing casualties, it was claimed.

There were no reports of damage or injuries inside Israel.

A string of mortar shells have struck the Golan during the 19-month long Syrian conflict between rebel fighters and forces loyal to President Bashar al Assad.

Israel's military chief, Lieutenant-General Benny Gantz, warned troops on the Golan Heights a week ago: "This is a Syrian issue that could become our issue."

The Jewish state captured the Golan from Syria in the 1967 Mid-East war.

Meanwhile, Israel's Prime Minister Benjamin Netanyahu said his country was "prepared to escalate" its response to Palestinian rocket fire, after one of the worst flare-ups along its border with Gaza in recent years.

The latest unrest began on Saturday evening when Gaza militants fired an anti-tank missile at an Israeli jeep along the Gaza border, injuring four soldiers, one of them severely.

Israel retaliated with air strikes, shelling and artillery fire that left six Palestinians dead and 35 injured by Sunday afternoon, and Palestinian militants fired at least 82 rockets into southern Israel.